$ F = \left[\begin{array}{rrr}0 & 1 & 2 \\ 2 & 1 & 0 \\ 2 & 2 & 1\end{array}\right]$ What is $ F^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}\frac{1}{2} & \frac{3}{2} & -1 \\ -1 & -2 & 2 \\ 1 & 1 & -1\end{array}\right]$